Water-soluble group 8 and 9 transition metal complexes containing a trihydrazinophosphaadamantane ligand:: Catalytic applications in isomerization of allylic alcohols and cycloisomerization of (Z)-enynols in aqueous medium

An optimized synthesis of the 2,4,10-trimethyl-1,2,4,5,7,10-hexaaza-3-phosphatricyclo- [3.3.1.1(3,7)]decane ligand (THPA) is described. It readily reacts with the dimers [{RuCl(mu-Cl(eta(6)-arene))(2)] and [{MCl(mu-Cl)(cod)}2] to yield the corresponding mononuclear complexes [RuCl2(THPA)(eta(6)-arene)] [arene = C6H6 (4a), p-cymene (4b), 1,3,5-C6H3Me3 (4c), C6Me6 (4d)] and [MCl(THPA)(cod)] [M = Rh (7a), Ir (7b)], respectively. Treatment of 4a and b with MeOTf affords the cationic derivatives [RuCl2)(THPA-Me) (eta(6)-arene)][OTf] {arene = C6H6 (5a), p-cymene (5b) THPA-Me = 1,2,4,10-tetramethyl-2,4,5,7,10-pentaaza-1-azonia-3-phosphatricyclo- [3.3.1.1(3,7)]decane}. The arene-ruthenium(II) complexes 4a-d and 5a and b are efficient catalysts for the redox isomerization of allylic alcohols into carbonyl compounds in both THF and aqueous media. The catalytic systems can be recycled by a simple extraction process and used in up to 4 consecutive runs. All the water-soluble complexes prepared in this work are able to promote the cycloisomerization of (Z)-enynols to afford furans in water, the best performance being obtained with the iridium catalyst 7b. Furthermore, 7b has shown an excellent recyclability (10 runs). This study represents the first example of iridium-catalyzed cycloisomerization of (Z)enynols.